Lightweight, portable, vibrating, concrete screeds of the type to which the present invention is generally related are described in applicant's prior U.S. Pat. Nos. 4,030,873, 4,213,749 and 4,253,778. The general state of the art is believed to be fully set forth in these references and therefore will not be restated except for pointing out certain prior art practices which primarily relate to the screed frame construction.
The present invention is primarily directed to the frame construction employed in vibrating screeds of the type described in applicant's prior patents. The improved frame construction of the invention is illustrated as embodied in an air-powered, vibrating, concrete screed.
As one aspect of the type of construction used in portable vibrating concrete screeds of the type to which the invention relates, it may be noted that the typical screed frame is made up of components which are welded together. Due to the stringent operating requirements and heavy wear encountered on the job, it is not uncommon for frame members to be bent or damaged and thus require replacement. An all-welded construction, of course, makes replacement of an individual frame component both time consuming and expensive.
Since the typical portable, concrete screed of the type to which the invention relates has a triangular cross section, it has become the practice to use a piece of ordinary steel pipe running lengthwise of the frame at the apex of the triangle and the frame braces are welded to this pipe. This pipe has also been used in air-vibrated concrete screeds as a conduit for carrying pressurized air and air vibrator hoses have been connected to the pipe as a means for supplying air to the vibrators. While the use of a pipe member of this type as both a structural member and as an air conduit is advantageous, a simple round pipe of this kind does not lend itself readily to the type of screed frame in which the members are bolted together for ease of replacement when damaged. Thus, there is a need for an improved screed frame adapted to be bolted together and employing an improved apex tube construction that both lends itself to serving as an air conduit as well as a structural member which can be easily bolted to other structural members for establishing a relatively rigid screed frame.
As a further aspect of screed constructions, it has been known to provide means enabling one screed section to be angled relative to another screed section to adjust to concrete pouring operations where a crown or valley shape is formed with the screed. However, it has not been known so far as applicant is aware to provide a screed frame construction in which a tubular member located at the apex of the triangular-shaped frame and adapted to serve as an air conduit and as a bolt securing structural member is also adapted to be used as a means for adjusting one screed section relative to another.
The object of the present invention thus becomes that of providing an improved frame construction for a vibrating-type concrete screed aimed at overcoming the shortcomings of prior screed frame constructions as discussed above and is illustrated embodied in an air-powered screed. Other objects will become apparent as the description proceeds.